The high‐pressure nitridation of nickel was investigated using a laser‐heated diamond‐anvil cell. Marcasite‐type nickel pernitride (NiN2) was synthesized at approximately 40 GPa, and it transformed into the tetragonal phase at approximately 3 GPa along with the decompression. The structural refinement of marcasite‐type NiN2 at 36 GPa gives an N‐N distance of 1.24 Å. The first‐principles calculation reveals that the marcasite‐type NiN2 is a narrow‐gap semiconductor, and high‐pressure in‐situ X‐ray diffraction measurements revealed a zero‐pressure bulk modulus of 172(6) GPa. The axial ratios (c/a and b/a) of marcasite‐type NiN2 are close to the upper‐limit values of marcasite‐type structures, which suggests that the stability of marcasite‐type transition metal pernitrides strongly depends on the d‐electrons.